England must decide whether to call up injury cover for Owen Farrell after their captain for the opening rounds of the Guinness Six Nations underwent thumb surgery.

Farrell has undergone a procedure to repair ligament damage and is expected to return to action in seven to 10 days, a timeframe that would enable him to play against Ireland in a fortnight.

However, with England departing for their pre-tournament training camp in Portugal on Wednesday his ability to take part in training could be severely restricted, throwing Eddie Jones' preparations into turmoil.

The worst case scenario would mean he is unable to take part in sessions until four days before the Aviva Stadium title showdown.

"Owen has been complaining – but not very much – about his hand being a bit sore," Saracens director of rugby Mark McCall said.

"We decided yesterday (Friday) to send him for a scan to make sure we know what he's got. We thought he was going to play today and it was after the scan that he was pulled out.

"It turned out to be a very minor problem with a tendon in his thumb. The procedure has already been done this morning.

"As far as I know he'll be back in seven days, something like that, so he should be able to play a full part in the Six Nations.

"I'm sure he will be going to Portugal because I think he'll be available for selection."

Jones, meanwhile, has entered the debate over spying on opponents in training ignited by the admission of Leeds manager Marcelo Bielsa that he has had all rivals in the Championship secretly watched by a member of his staff.

While Jones believes there was once a benefit in such subterfuge, he insists technology has made it redundant.

"Fifteen years ago we used to send people out in costumes to watch training," Jones said.

"I can remember sending a coach who is now in a very senior position now in a costume to go and watch one team play and he got chased out of there. He was dressed up like a swagman, wearing one of those hats with corks.

"Now you don't need to do that because you see everything in the game. I have been coaching for 20 years and it has always been going on. If you want to do that you can do it.

"I can say with a hand on my heart we don't do it any more. We just don't see the value of it because we can glean most of the stuff from the games."

If, as expected, Farrell is passed fit to play Ireland he will come face-to-face with his Lions team-mate Jonathan Sexton, who Jones believes is given preferential treatment from officials.

"Sexton is a reasonably big player who has the bat phone to the referee. He is the only one allowed to pick up the red phone to talk to the referee," Jones said.

"When he talks, the referee listens. That is because of his status in the game – you earn that, like Richie McCaw did."